Hi danielgc,
Hmmm - it looks like the PHP process crashes upon starting the database backup. (Which then happens on every retry too). That's an unknown issue - i.e. not seen before. Can you try disabling all your other plugins and see if that makes a difference?
Also, you could ask your web hosting company where your PHP error logs are stored. Often they are in a file called error_log which may be in the root of your WP site or in wp-admin. You could paste that for us too (just the ones from the right time-frame - not all since the beginning of time!).
If you do any PHP coding yourself, then you could go into wp-content/plugins/updraftplus/updraftplus.php and find the function backup_db() and insert lots of lines like $updraftplus->log("I am here (1)"); to try to see on which line the crash occurs.
David